|It would be close; have seen cards of this class work OK on a 250w psu. Have also seen them not work on a 300 or 350w. |
Some thoughts though...
...can you find a 1Gb HD 6670 for about the same price?
...you don't need a 2Gb flavor of the HD 6570. 1Gb is just fine.
...insure your vendor will let you return the video card without paying a restocking fee in case this doesn't work. You'll get better help if we know what we're working on.
You might post the make and exact model number of your machine or see if the label on the power supply states the amps on the +12v rail.